Carcinogenic N-alkyl-N-nitroso compounds cause a rapid and selective depletion of the nicotinamide adenine dinucleotide (NAD) pool of 3T3 cells by causing a rapid stimulation of degredative reactions of NAD. Studies using N-methyl-N-nitro-N-nitrosoguanidine (MNNG) have shown that MNNG greatly stimulates the conversion of NAD to the chromosomal polymer poly (ADP-ribose). The proposed studies will examine the relationship between NAD lowering and poly(ADP-ribose) synthesis in vivo. The relationship between carcinogens and mono(ADP-ribose) metabolism and degredation via NAD pyrophosphatase activity will also be studied. Experiments designed to study the relationship between poly (ADP-ribose) synthesis and DNA repair replication in normal and NAD depleted 3T3 cells will be done.